Objectives: a. Long terms goals The long term objective of this study is to investigate the biochemistry and physiology of the renin-angiotensin system in relation to circulatory homeostasis and fluid and electrolyte balance. Studies will be carried out in experimental animals and in normal and hypertensive man. The three specific short term objectives of the study will be: 1. A clearer understanding of the humoral determinants of renin release from the kidney of normal and hypertensive man. 2. A more precise knowledge of the mechanism of conversion of angiotensin I (AI) to angiotensin II (AII) in the pulmonary circulation, and thus of the most important mechanism of AII production. In the course of these studies, the structural requirements for cinding of AI to AI antibody will be studied and the mechanism of action of inhibitors of AI conversion will be examined in detail. 3. Investigation of disorders of AI conversion in man.